The invention concerns an apparatus for removing metal particles from a liquid. The invention particularly concerns such an apparatus where a bag filter is used, the liquid to be filtered is passed through the bag filter.
The use of liquids, such as cutting oil, to extend the life of metal working machinery and to maintain the work surfaces at a constant temperature is well known. With current environmental regulations, however, the used oil which contains metal particles cannot simply be discarded. By filtering the metal particles from the cutting oil, the cutting oil becomes reusable and thereby creates less hazardous waste.
Also, manufacturers of metal products that use an ELPO system ("electronic deposition of paint") have a recirculating paint bath that the metal products are submerged in wherein the paint pigment is electronically deposited on the metal. During the submersion of the products, metal slivers and weld balls are initially washed off the products and are then electronically deposited back on the products to show up as dirt in the paint. By using a filter bag with a particular micron size to maintain cleanliness specifications, dirt particles are removed, but by the nature of the metal particles, they are able to work themselves through the filter media and still contaminate the paint bath.
Various ways to remove metal particles from a liquid have been attempted. The most often used method was to place a series of magnets into a metal cartridge filter. It has been asserted that these metal cartridge filters are easily cleaned and the magnets easily replaced. However, many of the cartridge filters contain a pleated-paper filter which actually performs the filtration. It has become apparent the pleated-paper filters are not sufficiently resilient to withstand long-term use without tearing. The application of the cartridge filter is also limited by its shape, its inability to withstand high temperatures and low liquid flow rates.
It has also been suggested that simply placing a magnet in the bottom of a bag filter would be sufficient means to remove metal particles from a liquid. The problem with this method is that much of the liquid which passes through a bag filter exits from the sides of the filter. By only creating a small or localized magnetic force in the filter, much of the liquid passes through the filter uninfluenced by the magnetic force and, therefore, most metal particles are not removed from the liquid.
While being somewhat effective, the prior art has not achieved the desired results and still fails to solve many of the technical problems which previously existed. The metal cannister filters have been ineffective in preventing metal particles which have collected around the magnets from coagulating and breaking away from the magnetic force. In fact, the metal cartridges often become clogged with metal particles which have been removed from the liquid. The metal cartridge filters have also failed in their attempts to present a filter in which the magnets are easily replaced, and the filter is easily cleaned. In addition, the metal filters which contain a pleated-paper filter often tear and thus, cease to perform their filtration function.